RATE MODULATED PACING BASED ON RIGHT-VENTRICULAR DP DT - QUANTITATIVE-ANALYSIS OF CHRONOTROPIC RESPONSE/

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase wi th exercise workload. Thus, the maximum systolic dP/dt may be a potent ially useful sensor to control the pacing rate of a permanent pacing s ystem. The present study was designed to test the long-term performanc e of a permanent pacemaker that modulates pacing rate based on right v entricular dP/dt and to quantitatively analyze the chronotropic respon se characteristics of this sensor in a group of patients with widely v arying structural heart diseases and degrees of hemodynamic impairment . A permanent pacing system incorporating a high fidelity pressure sen sor in the lead for measurement of right ventricular dP/dt was implant ed in 13 patients with atrial arrhythmias and AV block, including indi viduals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septal defect, dil ated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VV IR pacing modes with measurement of expired gas exchange and quantitat ive analysis of chronotropic response using the concept of metabolic r eserve. The peak right ventricular dP/dt ranged from 238-891 mmHg/sec with a pulse pressure that ranged from 19-41 mmHg. There was a positiv e correlation between the right ventricular dP/dt and pulse pressure ( r = 0.70, P = 0.012). The maximum pacing rate and VO2max were 72 +/- 6 beats/min and 12.61 +/- 4.0 cc O2/kg per minute during VVI pacing and increased to 124 +/- 18 beats/min and 15.89 +/- 5.9 cc O2/kg per minu te in the VVIR pacing mode (P < 0.0003 and P < 0.002, respectively). T he integrated area under the normalized rate response curve was 96.7 /- 45.7% of expected during exercise and 100.1 +/- 43.4 % of expected during recovery. One patient demonstrated an anomalous increase in pac ing rate in response to a change in posture to the left lateral decubi tus position, Thus, the peak positive right ventricular dP/dt is an ef fective rate control parameter for permanent pacing systems. The chron otropic response was proportional to metabolic workload during treadmi ll exercise in this study population with widely varying forms of stru ctural heart disease.